EFFECTS OF STORAGE TEMPERATURE ON VITAL PARAMETERS OF CLINICAL GRADE CRYOPRESERVED MESENCHYMAL STEM CELL FINAL PRODUCT

Background & AimA potent off-the-shelf cell product that can be thawed and ready to be infused into the patients in a timely manner is essential for treatment of acute inflammatory diseases such as sepsis. The storage of mesenchymal stromal/stem cells (MSCs) in liquid nitrogen (LN) has been considered the standard practice. However, the cost and complexity of on demand cold-chain logistic for LN supplies prompted us to examine the impact of transfer storage in ultralow temperatures (-80°C) and -20°C on MSC final product compared to continuous storage in LN.Methods, Results & ConclusionWe performed a comprehensive analysis of cell viability, recovery, immunomodulatory activity and post-thaw in-use stability of a bone marrow derived MSC final product, cryopreserved at 6 million cell/mL in Plasmalyte-A supplemented with 5% human albumin and 10% DMSO. Products were cryopreserved in LN for over 4 weeks, before being transferred to -80 or -20°C freezer for 1 or 2 weeks.Post-thaw viability of MSC at 1 week, assessed by Trypan blue exclusion, was 93% in LN, 91% in -80°C and 7% in -20°C. Annexin V/Propidium iodine (AV/PI) staining showed 71% live cells for LN storage, 61% for -80°C and 3% for -20°C. Cell Recovery was at 77% in LN, 86% in -80°C, and 7% in -20°C. Results after 2-week storage also showed comparable viability in LN and -80°C ultralow freezer by Trypan blue staining (93% and 91%, respectively) or by AV/PI (70% and 65%, respectively). Cell recovery was also similar in LN and -80°C storage (95% and 88%, respectively ). In contrast, -20°C storage was unsuitable, yielding only 3% viable cells and 4% cell recovery. When seeded on culture plates, no observable morphological alteration was noted between cells in -80°C freezer vs. in LN for up to transient 2 weeks, while cells in -20°C showed minimal attachment. A comparable extent of T cell inhibition (26% and 20%) and improvement of monocyte phagocytosis (15% and 13%) were detected by MSCs stored in LN and -80°C, respectively, while MSCs from -20°C exerted no immunomodulatory effects.Thermal transition from LN to ultralow storage was well tolerated by MSC product for up to 2 weeks, demonstrated by comparable vital characterization and functionality parameters. Future study with larger volume and storage time beyond 2-week is warranted to better understanding of MSC product storage stability.